Question for Pano: JB's 605 OB crossovers

[Skip Pack]

I grabbed a copy of the schematic you posted on the crossovers
you used with John Busch's open baffle 605A speakers at LSAF
last May. I am using Jeff Markwart's design on my 605B OBs and
thought I'd try the fixed attenuation with HF compensation
you show in the LSAF design on the tweeter side. I'm curious why you
have the 10uf cap in parallel with the 4 ohm resistor on the ground
leg? It looks like it would have no effect as all frequencies that made
it though the 2nd order filter would be a good octave higher. Is this
intended to put a steeper, shelved cut from say 800 hz or so?

I've attached that schematic. Not sure how it will appear.

Thanks,

Skip

[Panomaniac]

Hi Skip,
Sorry I haven't been on the forum in quite some time.
Let me study your question and get back to you.

Pano

[Skip Pack]

Thanks for picking the question up. I just noticed the 'extra' cap
and was curious.

Skip

[donaldpatten]

SKIP

The two RC networks " boost " the HF to the horn.
Below the frequencys the caps kick in the HF driver ckt looks like 14R in series with an 8 ohm driver . About -9dB ,a reasonable padding down of the horn to match the woofer . At very HF the 3R and 4R are bypassed and the ckt looks like 7R and an 8 ohm driver. -5.5dB ,or 3.5dB of " boost " split by the RCs for high freqs.
I read the values as : 10uF & 4 ohms res freq = 4 kHz, and 0.47uF & 3 ohms freq = 113kHz?? Could the 0.47 be 4.7?? Then the second freq = 11kHz.

Don

[MANZANITA]

Bingo!

[Skip Pack]

Thanks to you both. I was looking at the RC pairs as a series
attenuator with the capacitor acting has an HF bypass. I'll
need to bone up on them as a resonant circuit element.
Also, just to confirm, the cap marked in the diagram as
.47 uf should be 4.7 uf? I have both, so I probably should
start with the right one.

SKip

[donaldpatten]

HI Skip
I would use a 4.7uF cap . Every one knows those drivers need all the help they can get.
When you build the XOs try them with all the resistors leaving out the 10 and 4.7 caps. Then add them in and tell us whsat you hear .
Don

[Skip Pack]

When you build the XOs try them with all the resistors leaving out the 10 and 4.7 caps. Then add them in and tell us whsat you hear .

That's a great idea. I have that basic crossover in effect already, with
the series cap and bypass inductor for the highpass, but with a big
pot for attenuation. I will ditch the pot and put in the series resistors
first to see how close the sound matches the pot (after measuring
the the legs on the pot), and then clip lead in the caps as a first
pass on the mod.

thanks,

Skip

[MANZANITA]

Skip Pack

Good to see you on the forum.

The Jeff Marquart base crossover is quite good. However, after listening to it I felt it needed to be adjusted to the actual 605's, especialy considering the way I was using them.

They were not stock with the GPA upgrades and of course the OB aspects. So it came down to adjusting by ear with some measurement to keep things from straying too far. Text book traps just did not seem to improve things. They are general at best.

So much listening, adjusting, listen again in several rooms with a wide range of music and amplifier - CD and phono sources. It takes trial and error to get things to the next level. No other easy way around it. Know that Pano was doing some of this at LSAF too.

So, would be iterested in knowing what is working, or not working for you. Your 05's sounded quite good in Sarcamento. Wish we could have listened to them a bit louder in a more appropriately sized room.

[Skip Pack]

Hello John,

Yeah, I figure it's parts box time. At least I have a pretty good
selection of cap values and varieties to try on these compensation
filter sections. It's the roomfull of coils that I lack. I'm currently
using the Erse Super-Q coils in these crossovers, but always wonder
what some big, quality air cores might do.

Skip